In recent years, the field of computer typesetting has inclined increasingly to the use of a cathode ray tube (CRT) for visualization of text and optical conveyance of the visualized text to a light-sensitive recording medium.
So-called "patchwork" is a practice common to various known schemes. In this practice, one defines a patch of the screen, i.e., a subdivision thereof, to be the area needed for the visualization of the largest single character to be recorded. On a horizontal CRT line basis, successive such patches are visualized, some involving presentation of the single largest character and other patches entailing presentation of a plurality of smaller characters which can fit the patch. As each patch is visualized, it is focused upon a recording medium. A recording lens is thus moved into registry with each visualized patch to effect full line recording. The recording medium is itself advanced transversely to the direction of lens movement to effect full page recording.
As patches are linewise accumulated, horizontal presentation nonuniformity becomes evident as equipment components vary in character, e.g., as amplifiers age, as resistors vary, as CRT high voltage changes, and as deflection yokes vary in beam deflecting characteristics. Thus, the most carefully initially trimmed system will remain in calibration only temporarily and the user must retrim to his evident productivity disadvantage and maintenance expense. Between retrimmings, the user may live with varying degrees of discernible patchwork. Prior to the subject invention, this labor intensive situation has been mollified only at the considerable expense of electronic components of quite high standards of tolerance which serve inherently to lessen patchwork discernibility. On the other hand, it would be a desiratum to have the retrimmings programable, e.g., to occur after each one hundred lines of text, or key-called by the operator at his option.